The designation had a promising start as a way to distinguish adult-only content, but 22 years later confusion reigns over rules and few have embraced it.

The only X-rated film to win an Academy Award for best picture, John Schlesinger's "Midnight Cowboy" (based on James Leo Herlihy's novel) starred then-newcomer Jon Voight, left, as a prostitute in New York City and Dustin Hoffman as his friend, an ailing thief.

"We felt the X rating was the correct rating for it," the film's producer Jerome Hellman told the L.A. Times in 1992. "X in those days did not mean pornography." After "Midnight Cowboy" won three Oscars (and was nominated for four more), it was re-rated R.

"The great thing about 'Midnight Cowboy' is that we didn't question what we were doing," Schlesinger told the Philadelphia Inquirer when the film was re-released in 1994. "We just did it with a total feeling of confidence and freedom. We didn't think, 'Oh, we're being very groundbreaking on this.' I just made the film the way I wanted to."

In the late '80s a thunderbolt of inspiration struck Jack Valenti, longtime chief of the Motion Picture Assn. of America: What if his organization got rid of the X rating, besmirched by years of misappropriation by hard-core exploitation films, and replaced it with a new marker that was both trademarked and respectable?

Thus was born the NC-17. Formally instituted in 1990, the restrictive rating aimed to signal moviegoers that a film included adult-oriented — but not necessarily pornographic — content and made those movies off-limits to anyone under 18.

Valenti had high hopes that the NC-17 — he called it "unstigmatized" — would usher in an era of mainstream acceptance for films with serious adult themes. But after some initial acceptance by directors, distributors, exhibitors and audiences, the rating fell deeply out of favor with filmmakers and moviegoers alike.

Now, even as basic cable is constantly pushing into ever-more steamy and violent territory and a wide variety of pornography is easily available on the Web, movie theaters are practically devoid of formally adults-only films. The number of movies released with the NC-17 rating has plummeted; those that do go out with that stamp do little business at the box office.

The reasons are clear: Some theater chains, including Cinemark, the nation's third-largest circuit, won't play them. A number of media outlets, particularly newspapers and television stations in more conservative states, won't accept advertising for them. Wal-Mart and other retailers won't sell copies on DVD.

Now at 22 years old — the same age as the X was when it was retired — the NC-17 is seen inside Hollywood and beyond as ineffective and broken. But no one can agree on how to fix it.

"There's no question there's a stigma," said Joan Graves, the head of the MPAA's ratings board. "If you have any ideas on how to break it, I'd love to hear them," she said, giving a small, not-entirely-happy laugh.

At issue is more than just what grade an industry trade group should assign to a particular movie, and more than questions of revenue and profit. At its core, the debate over NC-17 is a matter of what material society considers mainstream, who gets to make those determinations and what standards they use in doing so.

Out of favor

The NC-17's fall has been dramatic. Last year, just three such films arrived in theaters, and the highest-grossing, Fox Searchlight's sex-addiction drama"Shame," didn't even sell $4 million worth of tickets.

That's a far cry from the NC-17's promising beginnings in 1990, when more than a dozen films were released with the rating. Two of the first were serious art films: "Henry and June," about the romance between Henry Miller and Anais Nin, and "The Cook, the Thief, His Wife and Her Lover." They grossed $21 million and $14 million, respectively, in today's dollars.

The advent of the NC-17 coincided with an ambitious moment in American cinema — young auteurs such as Steven Soderbergh, Quentin Tarantino and Spike Lee were coming into their own, making movies that were adult in theme but artistic in style. It was possible to imagine these directors making films for adult audiences that would solidify the NC-17 as a rating just as acceptable as an R.

(After all, in its early days, the X generated some sizable hits — 1969's "Midnight Cowboy," which won best picture, took in $45 million, or $281 million in today's dollars; 1973's "Last Tango in Paris" made $36 million, or $225 million today).

But the NC-17 soon faltered. As signatories to the MPAA, the six major studios must release their films with ratings, and they began to get nervous about the commercial limitations of the NC-17. Potential mainstream NC-17 releases such as Paramount's Sharon Stone thriller "Sliver" (1993) were edited to land an R rating (which means children under 17 can be admitted, if accompanied by a parent or guardian).

A year later, Oliver Stone was given an NC-17 for "Natural Born Killers," as was Quentin Tarantino for "Pulp Fiction." Both re-cut their films so that they would end up with an R. (Both cinema history and the history of the NC-17 may well have unfolded very differently had "Pulp Fiction" gone out with an NC-17.)

The movies that did come out with an NC-17 — most notably Paul Verhoeven's über-campfest "Showgirls" (1995) — were so sufficiently silly and skin-filled that they only confirmed the perception that it was not a rating to be taken seriously.

Around 2004, there was a brief renaissance of NC-17 films. Lionsgate chose to release a French horror film called "High Tension" as NC-17 instead of unrated and Fox Searchlight took out Bernardo Bertolucci's art house drama "The Dreamers" as NC-17.

But that proved short-lived. Tom Bernard, the Sony Pictures Classics executive who was in charge of releasing Pedro Almodovar's "Bad Education" that year, said he was surprised by the opposition from media outlets and theater owners when he sought to bring out the movie as an NC-17. "The rating certainly hurt the box office," he said.

Smaller distributors who are not MPAA members have the option of releasing films given NC-17 ratings without any rating at all. (Among such films to have gone that route are Darren Aronofsky's "Requiem for a Dream,"Todd Solondz's "Happiness" and the Martin Lawrence concert film "You So Crazy." In 1995, Disney-owned Miramax set up an independent releasing entity for Larry Clark's "Kids" after it received an NC-17.) Increasingly, many filmmakers are choosing this course or are cutting their films to receive an R.